Structures that can be unfurled in space, of the solar array type for example, are generally made up of rigid panels articulated to one another, these panels, when in the stored position, being stacked on top of one another. These structures have the advantage of dynamics that are well controlled, but have the disadvantage of high specific mass and high inertia. Further, when in the stored position, the rigid structures occupy a significant amount of space under the fairing of a launcher. Because the space under the fairing of a launcher allocated to the unfurlable structures is limited, it is important to reduce the amount of space required by these unfurlable structures when they are in the stored position in order to optimize the area they can occupy when unfurled.
There are unfurlable flexible planar structures that comprise a flexible sheeting and tape springs which are fixed to one and the same plane of the sheeting. In the stored position, the sheeting and the tape springs are wound around a mandrel. The flexible planar structure is unfurled autonomously by the spontaneous unwinding of the tape springs when the mandrel is freed to rotate.
Indeed, as depicted in FIGS. 1a, 1b, 1c, tape springs are known in the field of space as being flexible tapes with a cross section in the form of a circular arc the radius of curvature of which is convex on a first face and concave on a second face, these tapes being able to pass from the wound state into the unwound state essentially as a result of their own stored elastic energy. Tape springs therefore have a natural tendency to unfurl in order to revert to their unwound state. If they are forced to refurl, they have a tendency to do so on a radius substantially equal to that of their transverse radius of curvature R. Only a small external force is therefore required in order to keep them wound in this shape. However, if this force suddenly disappears, the unfurling may be violent and uncontrolled, which means to say that the entire tape spring may have a tendency to straighten back out simultaneously over the entire length, and this presents a risk of damaging the flexible sheeting to which it is fixed, or surrounding elements. Conventional tape springs may thus present difficulties in terms of controlling their unfurling. Further, tape springs do not have the same stiffness on both the convex and concave faces 101, 102, their convex face 101 being flexible whereas their concave face 102 is rigid. The result of this is that in the unwound state, the slightest force, arrow in FIG. 1a, applied to the convex face 101 of the tape spring will have a tendency to cause the tape spring to flex whereas a force applied to the concave face 102 will have no effect, this presenting a problem of instability of the flexible structure in its unfurled state. In order to address this problem of stability in the unfurled state, it is therefore necessary to keep the sheeting in the unfurled position using an additional retaining device or to overengineer the tape spring in order to ensure that it remains stable under the forces of orbiting.